Fluctuations in serum steroid hormone concentrations and body mass during growth and sexual maturation in captive northern fur seals (<i>Callorhinus ursinus</i>)

Abstract

Northern fur seals (Callorhinus ursinus) have a distinct life history pattern comprising annual terrestrial breeding and oceanic migration, and the physiological changes associated with these patterns are of particular interest for understanding their environmental adaptations. However, owing to their oceanic distribution, limited information is available on the reproductive physiology of wild individuals during the immature stage and t he winter migration period. This study aimed to determine the relationships among the seasonal hormone profiles, body growth, age, and pregnancy using monthly serum samples collected over 3-5 years from two male and two female captive individuals during pubescence and sexual maturation. Small increases in the serum testosterone signaled puberty in males aged 3 and 4 years. Thereafter, males showed considerable increases in testosterone during breeding seasons, indicating sexual maturity. Immature female ser um progesterone was maintained at low levels, but after pubescence, females showed an increase in serum progesterone in August, the month next to the peak of delivery , followed by a decrease. In non-pregnant females, progesterone did not increase significa ntly until the next breeding season, but in pregnant females, they increased again from February to March and then gradually decreased. Immature males increased body mass constantly and reached puberty when their body mass exceeded 20 kg, and they showed s easonal weight fluctuations after puberty. These results provide fundamental information for determining sexual maturity and pregnancy in this species based on sex steroid hormones and body mass measurements.

Multi-omics analysis reveals changes in tryptophan and cholesterol metabolism before and after sexual maturation in captive macaques

“…Exploring the occurrence, processes, and judgment criteria of animal sexual maturity has important scientific and economic value for understanding physiological changes in species and guiding their reproduction. Various studies on sexual maturation have been conducted across a wide range of species, such as RM [ 2 ], Atlantic salmon ( Salmo salar ) [ 3 ], Atlantic bluefin tuna ( Thunnus thynnus ) [ 4 ], Carib grackle ( Quiscalus lugubris ) [ 5 ], macaroni penguin ( Eudyptes chrysolophus ) [ 6 ], northern fur seal ( Callorhinus ursinus ) [ 7 ], and wild boar ( Sus scrofa ) [ 8 ].…”